1. Field of the Invention
The invention relates to gyratory crushers and, more particularly, to gyratory crushers of the type having a crushing head mounted on an eccentric main shaft and incorporating a mechanism to prevent the main shaft and crushing head from spinning in the absence of a crushing load.
2. Discussion of the Related Art
Gyratory or cone crushers (sometimes known as gyrasphere crushers) are well known for crushing stone. A typical gyratory crusher includes 1) a stationary frame, 2) a generally conical crushing head mounted for rotation about an eccentric main shaft and including an upwardly facing convex crushing surface, and 3) an annular crusher bowl or concave that is mounted in the frame above the crushing head so as to define a crushing gap forming an annular crushing chamber. Eccentric rotation of the main shaft is effected by rotatably mounting the shaft on the crusher's main drive gear or bull gear on an axis which is offset from and inclined with respect to the axis of rotation of the main drive gear.
During a crushing operation, the crushing head, through the material being crushed, is placed in rolling engagement with the concave or crusher bowl and thus rotates, relative to the stationary frame and the main drive gear, in a direction opposite to the direction of main drive gear rotation. The crushing head and main shaft are mounted so as to be freely rotatable within the main drive gear to accommodate such relative rotation. However, in the absence of a crushing load, the crushing head tends to "spin" or rotate in the same direction and at the same speed as the main drive gear. When material to be crushed is fed into the crushing cavity and contacts the freely spinning crushing head, the material detrimentally abrades the crushing head and also the concave, both of which are typically formed from a relatively soft manganese liner. Initial contact between the stone or other materials to be crushed and the freely spinning head also can result in ejection of small and even some relatively large stones from the crusher, risking damage to external components of the crusher or injury to personnel in the vicinity of the crusher.
Many so-called "anti-spin" mechanisms have been proposed to eliminate or at least inhibit free spinning of an unloaded crushing head. Examples of such anti-spin mechanism are disclosed in U.S. Pat. No. 3,207,449 to Johnson; 3,743,193 to DeDiemar et al.; U.S. Pat. No. 3,750,809 to DeDiemar et al.; U.S. Pat. No. 4,206,881 to Werginz; U.S. Pat. No. 4,467,971 to Schuman; and U.S. Pat. No. 4,666,092 to Bremer. All of these patents disclose anti-spin mechanisms employing hydraulic brakes or some other device located near the upper end of the main shaft, i.e., within the crushing head, to resist or prevent crushing head spinning. The anti-spin mechanisms disclosed in all of these patents therefore are incompatible or at least ill-suited for use with a solid main shaft or one lacking a large internal axial bore.
Apart from problems of complexity and incompatibility with many eccentric shafts, another problem associated with many of the anti-spin mechanisms disclosed by the patents listed above is that the length of the main shaft and associated drive elements must be increased substantially to accommodate the anti-spin mechanism, leading to a significant increase in the overall axial height of the crusher. This represents a problem because crushers form but one component of a quarry system and must be sized to be compatible with augers, elevators, and conveyors commonly employed in quarry systems.
Still another problem associated with the anti-spin mechanisms disclosed in many of the patents listed above is that they are not very robust and cannot survive the severe vibrations and shock loads imposed on the mechanisms during crushing for prolonged periods of time. Moreover, many of these mechanisms are relatively inaccessible and difficult to install initially and to replace when they fail.
Yet another problem associated with many heretofore available anti-spin mechanisms is that they can never permit rotation of the main shaft and crushing head in the same direction that the main drive or bull gear rotates. Accordingly, if the crushing head becomes jammed due, e.g, to the introduction of non-crushable materials (known as tramp) into the crusher, the anti-spin mechanism and/or other components of the crusher are destroyed.
Some of these problems can be understood by a more detailed review of specific prior art references.
For instance, an overrunning clutch-based anti-spin mechanism is disclosed in the Johnson patent. The overrunning clutch is connected to the main shaft by a sliding coupling that permits relative sliding movement between the main shaft and the overrunning clutch but that prohibits relative rotational movement therebetween. The overrunning clutch includes 1) an input shaft coupled to the head and 2) a one-way clutch element that is coupled to the input shaft and that permits main shaft rotation in the crushing direction while prohibiting main shaft rotation in the spinning direction.
The anti-spin mechanism disclosed in the Johnson patent exhibits notable drawbacks. For instance, the sliding coupling is located within the upper portion of the crushing head and hence is incompatible for use with a solid main shaft or one lacking a large internal axial bore. Moreover, the one-way clutch element is incapable of permitting main shaft rotation in the spinning direction. A separate brake or shear pin therefore must be provided to permit shaft rotation in the spinning direction in the event that tramp becomes lodged in the crushing gap.
An exemplary hydraulic brake is disclosed in the Werginz '881 patent. The Werginz '881 patent discloses a main shaft that is rotationally coupled to a bidirectional hydraulic motor. The hydraulic motor is disposed in a hydraulic circuit including 1) an unpressurized reservoir (typically filled with lubricating oil also used to lubricate the main shaft and other components of the crusher), 2) a check valve, and 3) a relief valve. Rotation of the main shaft in the crushing direction causes oil to circulate from the reservoir upwardly through the check valve and back to the reservoir without imparting any substantial resistance to hydraulic motor rotation. However, hydraulic motor rotation in the opposite direction is resisted by the check valve which prevents fluid flow through the circuit in that direction. Limited fluid flow around the check valve is possible only when the fluid pressure generated by the rotating motor exceeds a value at which the relief valve opens, thereby permitting limited motor rotation and preventing damage to the hydraulic brake in the event that the crushing head becomes jammed by tramp.
While the hydraulic brake disclosed in the Werginz '881 patent is generally effective, it is relatively slow to react to main shaft spinning due to the fact that the hydraulic fluid is not pressurized before it is drawn into the hydraulic motor. Motor leakage and other factors therefore permit an air cushion to form at the inlet side of the hydraulic motor. This air cushion delays the response of the hydraulic motor to main shaft spinning because the hydraulic motor can rotate in the spinning direction until the air cushion is eliminated. By this time, the main shaft has built up substantial inertia and hence requires higher braking forces then would be required if shaft rotation in the spinning direction is prevented altogether. The hydraulic motor therefore must be oversized. In addition, the risk of damage to crusher components is increased because substantial shock loads are imposed on those components during rapid deceleration of the rotating main shaft. At least some of these problems are exacerbated by the fact that the hydraulic motor is rotating at the same low velocity as the main shaft (typically about 10-20 RPM) and cannot always generate adequate pressure for effective braking.